Vaccination is a powerful tool for improving human health. By contributing to the education of the immune system, vaccination has pioneered the fight against infectious diseases caused by pathogens such as bacteria.
Streptococcus pneumoniae is a Gram-positive bacterium and one of the main pathogens causing invasive diseases. 90 serotypes of Streptococcus pneumoniae have been identified based on difference in their core capsular polysaccharides (CPS) structures consisting of polymer of repeating oligosaccharides units, which are the virulent factor of the bacteria. Streptococcus pneumoniae type 3 (SP3) is part of the current pneumococcal vaccines consisting of isolated CPS (PPV-23 valent and PCV-13 valent). The capsular polysaccharide (CPS) of SP3 consists of [→3)-β-D-GlcpA-(1→4)-β-D-Glcp-(1→] repeating units. The commercially available 23-valent pneumococcal polysaccharide vaccine (PPV) contains purified capsular polysaccharide (CPS) antigens of 23 serotypes. However, this vaccine is not effective in the case of infants and young children. PCV-13 contains immunogenic conjugates comprising the purified polysaccharides of 13 different S. pneumoniae serotypes covalently linked to a protein, such as CRM197.
The currently marketed vaccines are effective in North America and Europe for individuals of a particular age. The manufacturing process for these vaccines is complex and results in a higher price. Therefore, the vaccine is unaffordable in most developing countries.
The glycosphingolipid α-galactosylceramide, also known as KRN7000, is a synthetic derivative of a glycolipid found in marine sponges, and identified as an immune activator that lowered the tumor burden of mice. This glycosphingolipid is known to be presented by antigen-presenting cells (APCs) by loading it unto the protein CD1d. After being loaded with the glycolipid, CD1d will interact with an invariant T-cell receptor (TCR) of invariant natural killer T cells (iNKT cells), resulting in the activation of the iNKT cells, expansion of their population, and secretion of a plethora of cytokines. A variety of α-galactosylceramide analogs able to stimulate iNKT cells were described in the literature (X. Li et al. PNAS 2010, 107, 29, 13010-13015). Also, αGalCer or analogs are being investigated in many contexts as vaccine adjuvants (U.S. Pat. No. 7,771,726 B2; WO 2006027685 A2). L. Bai et al. PNAS, 2013, 110, 40, 16097-16102 discloses that elevated IgM and IgG titers against pneumococcal capsular polysaccharide of SP14 are raised by immunizing mice with liposomes co-expressing the tetrasaccharide repeating unit of S. pneumoniae capsular polysaccharide serotype 14 linked to diacylglycerol and the NKT ligand PBS57. WO 2007/051004 A2 provides a conjugate comprising α-galactosylceramide conjugated at C-2 position of the galactose moiety via a linker to p-hydroxy-m-nitro phenyl antigen (NP-α-GalCer). Immunization of mice with said conjugate stimulated a strong antibody response specific for NP. To the best of our knowledge, no work has focused on covalently linking a glycosphingolipid to a saccharidic antigen of defined length.
It is the objective of the present invention to provide peptide-free and protein-free fully synthetic conjugates of general formula (I) comprising a Streptococcus pneumoniae type 3 capsular polysaccharide related carbohydrate of defined length covalently linked to a glycosphingolipid and pharmaceutical compositions thereof, useful for prevention and/or treatment of diseases associated with Streptococcus pneumoniae, and more specifically of diseases associated with Streptococcus pneumoniae type 3. Said conjugates and compositions thereof are heat-resistant or heat-stable. Immunization with said conjugates results in the production of high titters of antibodies against pneumococcal capsular polysaccharide of SP3. The antibodies present opsonophagocytosis activity and bactericidal activity.
The objective of the present invention is solved by the teaching of the independent claims. Further advantageous features, aspects and details of the invention are evident from the dependent claims, the description, the figures, and the examples of the present application.